Flat spot BS34

[01ps]

Question about a flat spot I am getting. When accelerating hard, I get plenty of jam up to I'd say 5-6000 rpm (no tach so just an educated guess). Suddenly it acts like it is starting to run out of fuel. I am not getting a flat spot when the throttle is wide open no matter the rpm, but instead it pulls hard up to 5/6000 then starts to lose power and sputter, meaning it is rpm related, not throttle related.

Now, would this indicate a low float level possibly?

I have open pipes and clamp on filters, but have already changed my pilot up a size and my mains up 2 sizes I think, and tried a few other combos. I have played around with my needle positions and it does not seem to make a difference. I set the floats the best I could but my manual is for a different carb I think cause the measurements are way off. The carbs are synced and it starts first kick. Can drive away immediatly after starting with full choke, and have it at half choke in 30 sec on a warm day, no choke in a minute. In other words, there are no other symptoms.

I don't think it is an ignition issue, but I could be wrong.

Any suggestions? Or any tips on setting float level? Mine are the black plastic floats, if that means anything.

Thanks

 

[JARichmond]

You may not think it's an ignition problem, but if you have the means to check your timing advance then I suggest you do so. Won't hurt, so why not eliminate another possibility off the drawing board.

 

[danisawesome]

I'm definitely no expert at carbs (yet!), but here's my input regardless. Since you're having problems at a certain RPM, it seems to me like maybe it's a jetting issue. I would take a look at your plugs after going out for a ride up in that RPM range and see if you're running lean or rich. My guess is that with open pipes and pods you may need to bump your main jets up one more size from stock (a total of 3 up on mains). Since you seem to be fine otherwise, I would leave the pilot and needle alone for the moment. I have my float height set at I think 26 or 27mm (without the gasket in place), which I found after searching the forums due to every manual varying a little bit.

And I agree with JARichmond, might as well check that stuff too while you're diagnosing stuff. Sometimes it can be a mix of a couple small things rather than one obvious solution.

 

[01ps]

My ignition is electronic so advance is controlled by the ignitor box, is it not? I did check the static timing awhile back and it was ok but I'll check it again.

 

[jmd_forest]

Yes, with the electronic ignition the "advance" is controlled by the ignitor box. Even though you did a static check, try checking the timing with the engine running, per the manual. I believe it is set to the "LF" mark on the rotor at 1200 RPMs.

 

[walleye]

Question about a flat spot I am getting. When accelerating hard, I get plenty of jam up to I'd say 5-6000 rpm (no tach so just an educated guess). Suddenly it acts like it is starting to run out of fuel. I am not getting a flat spot when the throttle is wide open no matter the rpm, but instead it pulls hard up to 5/6000 then starts to lose power and sputter, meaning it is rpm related, not throttle related.

Now, would this indicate a low float level possibly?

I have open pipes and clamp on filters, but have already changed my pilot up a size and my mains up 2 sizes I think, and tried a few other combos. I have played around with my needle positions and it does not seem to make a difference. I set the floats the best I could but my manual is for a different carb I think cause the measurements are way off. The carbs are synced and it starts first kick. Can drive away immediatly after starting with full choke, and have it at half choke in 30 sec on a warm day, no choke in a minute. In other words, there are no other symptoms.

I don't think it is an ignition issue, but I could be wrong.

Any suggestions? Or any tips on setting float level? Mine are the black plastic floats, if that means anything.

Thanks[/Q

 

[walleye]

The BS34's you have are the later ones that were also used on the xs650.
I have the same ones and the float height is 22mm off the gasket seat.
Hope this helps.